The present invention relates to the filed of surface scanning or imaging and more particularly to a system and method for scanning an image of an object in motion, wherein said scan remains in focus despite the motion of the object. The object comprises a plurality of walls defining a substantially rectangular shape. Such objects may for example comprise mail pieces or parcels. Hereinbelow, the present invention will be discussed with respect to scanning a substantially rectangular parcel, however, application of the present invention is not limited to only this application, nor are objects, as used above, limited to only mail pieces or parcels. The above walls further comprise surfaces to be scanned. The surfaces may be characterized as leading and trailing as with respect to a direction of conveyance. A top or lateral surface of the parcel may also be subject to scanning, the lateral surface being substantially perpendicular to the leading and trailing surfaces, as well as lateral side surfaces abutting the aforementioned surfaces.
According to the present invention, the parcels are conveyed pass at least one camera's field of view. The conveyance is performed by a conveyor belt or the like and make occur at a constant or varying speed. Each of the at least one camera comprises an optoelectronic sensor array, such as a charged coupled device or CCD, a zoom objective including a fast adjustable zoom mechanism, and auto focus. Furthermore, at least one control unit is provided for effecting adjustment signals to the camera(s); and at least one sensor unit for determining a position of the parcels with respect to predetermined locations along the conveying path and in dependence of a particular path are used. The camera(s) are fixed above or on a lateral side of the path and parcels aligned and further diagonally to the respective parcel surface(s) to be recorded.
Parcels are automatically sorted and distributed according to distribution information located on the parcel surface. The distribution information may comprise receiver addresses or bar code information. The parcels are set out on the conveying path with a relatively high speed, for example 2 m/sec, and on occasion very small distances therebetween. Accordingly, they are directed past a device for picture recording which makes the recorded pictures available to an OCR reader.
Because it is unknown from the start on which surface of the parcel the distribution information is located, all parcel surfaces must to be recorded with an automatic system to ensure proper handling. In this regard, it is known from EP 462 256 B1 to record all six faces of a rectangular object. From below, the recording is effected with a CCD line camera active during overhead passage of the object. Herein the parcel bottom always has a defined position and distance with respect to the camera. The remaining exposed surfaces are recorded with surface cameras. Because the rectangular objects have relatively large surfaces, the respective surface cameras need to have a very high resolution in order to effectively read present distribution information (e.g. addresses). For such cameras, which are very expensive and typically not available, the reading process is carried out in two stages. First, the entire surface is recorded in a low resolution to determine the presences of an address. Subsequently, in a second stage, only the address is scanned in a high resolution.
In patent abstracts of Japan vol. 014, no. 438 (P-1108), Sep. 19, 1990 and JP 02 171883 A (NEC Corp.), Jul. 3, 1990, a device for picture recording of object surfaces having distribution information thereon is disclosed. Herein, a camera is aligned normally (vertically) to the object surface to be recorded. The camera contains a CCD sensor and a lens for shooting, with at least one sensor, the measurement of the heights of the objects. A control unit is provided for the production of regulating signals for the camera in dependence of the measured object height. Furthermore, transport means are provided for the continuous transport of square objects past the camera. The camera is equipped with a zoom objective having a fast zoom adjusting mechanism as a lens for shooting, and is further equipped with auto focus. The fast zoom adjusting mechanism is directed by the control unit in such a way that the image scale, independent of previously measured object heights, remains constant.
It is also known that the zoom adjusting mechanism contains a linear motor (patent abstracts of Japan vol. 1997, no. 01, Jan. 31, 1997 & JP 08 248291 A (Sony Corp.), Sep. 27, 1996).
If one wants to record the front and rear faces or surfaces of square objects, the surfaces approximately aligned to the transporting direction and follow one another in close succession, then the camera(s) have to be directed from above or lateral side so as to overcome obstructed views from neighboring objects. For this task, very expensive zonal cameras with a high pixel number or line cameras are used, although image distortions and modifications of the resolution can occur. As such a need exists for a less expensive and effective system and method for scanning an object surface.